#define  _CRT_SECURE_NO_WARNINGS

#include<stdio.h>


double fun(long long n)
{
    if (n == 1)
        return 1.0;
    else if (n == 2)
        return 1.0;
    else
        return fun(n - 1) + fun(n - 2);
}
int main()
{
    long long n = 0;
    scanf("%lld", &n);
    if (n < 20)
        printf("%.8lf\n", fun(n) / fun(n + 1));
    else
        printf("0.61803399\n");

    return 0;
}